Our earlier investigations show that highly conjugated chelates incorporating cobalt-57, such as vitamin B12 and cobalt phthalocyanine escape fragmentation in 100 per cent of the Auger events. Consequently, the 14.4 keV Mossbauer gamma-emission conveys information regarding the chemical environment of the daughter iron-57. We have found variations in the Mossbauer parameters, the isomer shift and quadrupole splitting, of vitamin B12 and its derivatives, when axial ligands are varied with respect to their electron-donating power. We propose to make a systematic study of cis- and trans- effects. Measurements of isomer shifts will fill in an important gap by providing a direct measure of the variation in electron density at the metal atom. It should also be possible to characterize the electronic configurations of vitamin B12r and B12s. They play an important role in biological reactions. It would be particularly interesting to look for a transition from 6- to 5- coordination Co(III) corrinoids using stronger electron donors in the X-position. The transition is likely to be associated with a relative change in the Debye-Waller factor (recoil-free fraction) and also an enhancement of the anisotropy of the amplitude of vibration of the central metal atom in the axial direction with respect to the equatorial plane. If the transition from 6- to 5- coordination is confirmed, this feature would be of particular significance in biological reactions of vitamin B12 coenzyme. Emission Mossbauer spectroscopy would be especially valuable for investigating enzymic reactions, because of its high sensitivity. Different models, invoking formation of specific species like enzyme bound vitamin B12s or B12r, methyl-B12-enzyme, Co to S linkage in cobamide or rupture of Co to C bound in the coenzyme, and complexes of the cobalt atom of B12 with either substrate or product, can be verified.